Microphone Basics

A microphone is a transducer that converts acoustical energy to electrical energy. There are two types of microphones at Media Loan: dynamic and condenser. Dynamic mics are very rugged and can handle high sound pressure levels. They are slower to respond to transients. Condenser mics are more sensitive and can pick up faster transients. They also require power. All of the condensers available in General Access can be powered by a battery. Some of the condensers can be powered from phantom power. Phantom power is a power source that is supplied through the mic cable from a mixer. Media Loan has mixers available for checkout that can supply phantom power. Zoom H4n and Olympus LS-100 field recorders are also capable of supplying phantom power.

Pickup Patterns

All microphones respond to sound differently based on direction. This is called the microphone’s pickup or polar pattern. The shape of the pattern tells you how sensitive the mic is to sound approaching from one direction. There are 3 basic patterns:

OMNI-DIRECTIONAL, BI-DIRECTIONAL and UNI-DIRECTIONAL The uni-directional category is broken down into cardioid, supercardioid, and hyper-cardioid. An OMNI-DIRECTIONAL mic picks up sound from all directions.
A BI-DIRECTIONAL mic picks up sound from either side of the mic. There are no BI-DIRECTIONAL mics in Media Loan’s General Access equipment but some stereo mics make use of a BI-DIRECTIONAL element.
CARDIOID mics pick up sound in a heart shaped pattern in front of the mic. This allows you to focus on one sound while excluding other sounds. Also all directional mics are omni directional with low frequencies. This means that a cardioid mic may pick up low frequencies outside of it’s pick up pattern.
SUPER-CARDIOID mics have a narrower pattern in the front but they also have a small lobe in the back of the pattern.
HYPERCARDIOD, or shotgun mics have a very narrow pattern in the front. They have a rear lobe like the supercardioid but they also have lobes on the side of the mic. They are used to focus in a specific direction. You need to pay attention to the side lobes. If you are standing next to a noisy camera with a shotgun mic the side lobes might pick up the camera along with the intended sounds.

OMNI
BI-DIRECTIONAL
CARDIOID
SUPER-CARDIOID
HYPERCARDIOID

Proximity Effect

When most uni-directional microphones are placed close to a sound source the bass frequencies increase in level. This is called the proximity effect. Sometimes this is desired. People may speak into a mic that is close up to get a deeper sound out of their voice. Sometimes you may not want this sound. If you are recording some one who moves back and forth from the mic too much the bass sound of their voice may not be even. Some cardioid microphones are designed to eliminate the proximity effect. The EV RE-15, RE-16 and RE-18 are designed this way. They have a row of slots down the side of the mic. If they are covered up there will be the proximity effect. So be careful how you hold the mic.

Balanced Audio and Hi/Lows

Audio signals can be carried on two types of cables; balanced and unbalanced. A balanced cable use two wires for the audio signal and one for the shield. The 3 pin XLR connector of a mic cable is the most common example of a balanced cable. An unbalanced cable has one wire for the audio signal and one wire for the shield. Balanced signals are less likely to pick up extra noise and can be run for hundred’s of feet if needed. Unbalanced signals are more likely to pick up noise but they are okay to use for short distances. Most of the mics at Media Loan use balanced XLR connectors. A few of the mics have an unbalanced cable with a mini or 1/4” connector. Most of our recording equipment uses unbalanced mini or 1/4” inputs. To convert from a balanced to an unbalanced signal you need a transformer and Media Loan calls its adaptors with transformers hilows. You need a hi-low to plug a mic with an XLR connector into a device with a mini input. This keeps the audio balanced from the mic to the hi-low. There is only a short section of unbalanced signal from the hi-low to the recorder. Media Loan has 1/4” and mini hi-lows. Make sure that the you get the right type for your needs. Also, all of the mini hi-lows look like a stereo connector but they are really mono. If you use a hi-low with a stereo device like a mini-disc recorder or palmcorder it may only record to one of the 2 tracks and you will only hear it in one side of the headphones.

Levels

A microphone generates a very low level signal. It always needs to be amplified before we can use it. A mic level signal can range from -60 to -20db. The level of signal from devices such as vcrs and cassette decks is -10db. Some recorders have a special mic input which amplifies the mic signal to line level. If you plugged a CD player output into a mic input it would sound distorted. Some recorders such as the 4-track cassette recorders have inputs that can take a mic or line signal. But there is a mic preamp control on the recorder. It’s normally called the trim control. You need to adjust this to set levels with a microphone.

LEVELS CHART

Filters

Some of the microphones have hgh pass filters. A filter removes specific frequencies from the audio signal. A high pass filter removes the low frequencies and is also called a bass roll off or low cut filter. A low pass filter removes the higher frequencies and is also called a high cut. Normally, you should wait until the recording process is complete to perform drastic equalization, but sometimes during recording the low frequenies will be unwanted noise like wind or the microphone shaking. When this is the case, it can improve the recording to cut out the lower frequecies. The Sennheiser 421 has a 5 position bass roll off switch. The EV RE-15 and RE-16 have a two position switch. Media Loan also has several XLR barrels that operate as high or low pass filters between the microphone and the recorder.

Media Loan's General Access Microphones

We have a catalog of Microphones in General Access with information about each mics polar pattern, transducer type, uses and other useful information.